Constraints on the trilinear Higgs self coupling from precision observables

We present the constraints on the trilinear Higgs self coupling that arise from loop effects in the $W$ boson mass and the effective sine predictions. We compute the contributions to these precision observables of two-loop diagrams featuring an anomalous trilinear Higgs self coupling. We explicitly show that the same anomalous contributions are found if the analysis of $m_{ \scriptscriptstyle W}$ and \mbox{\sin^2 \theta^{{\rm lep}}_{{\rm eff}}} is performed in a theory in which the scalar potential in the Standard Model Lagrangian is modified by an (in)finite tower of $(\Phi^\dagger \Phi)^n$ terms with $\Phi$ the Higgs doublet. We find that the bounds on the trilinear Higgs self coupling from precision observables are competitive with those coming from Higgs pair production.Comment: 23 pages, 4 figures; V2: References added, version published on JHE

Effective cosmological constant induced by stochastic fluctuations of Newton's constant

We consider implications of the microscopic dynamics of spacetime for the evolution of cosmological models. We argue that quantum geometry effects may lead to stochastic fluctuations of the gravitational constant, which is thus considered as a macroscopic effective dynamical quantity. Consistency with Riemannian geometry entails the presence of a time-dependent dark energy term in the modified field equations, which can be expressed in terms of the dynamical gravitational constant. We suggest that the late-time accelerated expansion of the Universe may be ascribed to quantum fluctuations in the geometry of spacetime rather than the vacuum energy from the matter sector.Comment: 10 pages, 1 figure, v2: added legend in Fig.1 and a referenc

Generic Loop Effects of New Scalars and Fermions in b→sℓ+ℓ−b\to s\ell^+\ell^-, (g−2)μ(g-2)_\mu and a Vector-like 4th4^{\rm th} Generation

In this article we investigate in detail the possibility of accounting for the $b\to s\ell^+\ell^-$ and $(g-2)_\mu$ anomalies via loop contributions involving with new scalars and fermions. For this purpose, we first write down the most general Lagrangian which can generate the desired effects and then calculate the generic expressions for all relevant $b\to s$ Wilson coefficients. Here we extend previous analysis by allowing that the new particles can also couple to right-handed Standard Model (SM) fermions as preferred by recent $b\to s\ell^+\ell^-$ data and the anomalous magnetic moment of the muon. In the second part of this article we illustrate this generic approach for a UV complete model in which we supplement the Standard Model by a $4^{\rm th}$ generation of vector-like fermions and a real scalar field. This model allows one to coherently address the observed anomalies in $b\to s\ell^+\ell^-$ transitions and in $a_\mu$ without violating the bounds from other observables (in particular $B_s -\bar B_s$ mixing) or LHC searches. In fact, we find that our global fit to this model, after the recent experimental updates, is very good and prefers couplings to right-handed SM fermions, showing the importance of our generic setup and calculation performed in the first part of the article.Comment: 44 pages, 10 figures, 7 table

B→K∗ℓ+ℓ−B\to K^* \ell^+ \ell^- decays at large recoil in the Standard Model: a theoretical reappraisal

We critically reassess the theoretical uncertainties in the Standard Model calculation of the $B \to K^* \ell^+ \ell^-$ observables, focusing on the low $q^2$ region. We point out that even optimized observables are affected by sizable uncertainties, since hadronic contributions generated by current-current operators with charm are difficult to estimate, especially for $q^2 \sim 4 m_c^2\simeq 6.8$ GeV$^2$. We perform a detailed numerical analysis and present both predictions and results from the fit obtained using most recent data. We find that non-factorizable power corrections of the expected order of magnitude are sufficient to give a good description of current experimental data within the Standard Model. We discuss in detail the $q^2$ dependence of the corrections and their possible interpretation as shifts of the Standard Model Wilson coefficients.Comment: 33 pages, 7 figures, 11 tables. v2: fixed numerical error in S4 and typos; added discussion of the impact of future measurements; conclusions unchange

On Flavourful Easter eggs for New Physics hunger and Lepton Flavour Universality violation

Within the standard approach of effective field theory of weak interactions for $\Delta B = 1$ transitions, we look for possibly unexpected subtle New Physics effects, here dubbed "flavourful Easter eggs". We perform a Bayesian global fit using the publicly available HEPfit package, taking into account state-of-the-art experimental information concerning these processes, including the suggestive measurements from LHCb of $R_{K}$ and $R_{K^{*}}$, the latter available only very recently. We parametrize New Physics contributions to $b \to s$ transitions in terms of shifts of Wilson coefficients of the electromagnetic dipole and semi-leptonic operators, assuming CP-conserving effects, but allowing in general for violation of lepton flavour universality. We show how optimistic/conservative hadronic estimates can impact quantitatively the size of New Physics extracted from the fit. With a conservative approach to hadronic uncertainties we find nonzero New Physics contributions to Wilson coefficients at the level of $\sim 3\sigma$, depending on the model chosen. Furthermore, given the interplay between hadronic contributions and New Physics effects in the leptonic vector current, a scenario with nonstandard leptonic axial currents is comparable to the more widely advocated one with New Physics in the leptonic vector current.Comment: 27 pages, 6 figures and 5 tables. v2: numerical results and plots replaced with higher statistics MC runs, references added. v3: final version to appear in EPJ

The CKM parameters in the SMEFT

The extraction of the Cabibbo-Kobayashi-Maskawa (CKM) matrix from flavour observables can be affected by physics beyond the Standard Model (SM). We provide a general roadmap to take this into account, which we apply to the case of the Standard Model Effective Field Theory (SMEFT). We choose a set of four input observables that determine the four Wolfenstein parameters, and discuss how the effects of dimension-six operators can be included in their definition. We provide numerical values and confidence intervals for the CKM parameters, and compare them with the results of CKM fits obtained in the SM context. Our approach allows one to perform general SMEFT analyses in a consistent fashion, independently of any assumptions about the way new physics affects flavour observables. We discuss a few examples illustrating how our approach can be implemented in practice.Comment: 36 pages. Version published in JHE

Renormalisation group analysis of scalar Leptoquark couplings addressing flavour anomalies: emergence of lepton-flavour universality

Leptoquarks with masses between 2 TeV and 50 TeV are commonly invoked to explain deviations between data and Standard-Model (SM) predictions of several observables in the decays $b\to c\tau \bar\nu$ and $b\to s \ell^+\ell^-$ with $\ell=e,\mu$. While Leptoquarks appear in theories unifying quarks and leptons, the corresponding unification scale $M_{QLU}$ is typically many orders of magnitude above this mass range. We study the case that the mass gap between the electroweak scale and $M_{QLU}$ is only populated by scalar Leptoquarks and SM particles, restricting ourselves to scenarios addressing the mentioned flavour anomalies, and determine the renormalisation-group evolution of Leptoquark couplings to fermions below $M_{QLU}$. In the most general case, we consider three SU(2) triplet Leptoquarks $S_3^\ell$, $\ell=e,\mu,\tau$, which couple quark doublets to the lepton doublet $(\nu_\ell,\ell^-)$ to address the $b\to s \ell^+\ell^-$ anomalies. In this case, we find a scenario in which the Leptoquark couplings to electrons and muons are driven to the same infrared fixed point, so that lepton flavour universality emerges dynamically. However, the corresponding fixed point for the couplings to taus is necessarily opposite in sign, leading to a unique signature in $b \to s\tau^+\tau^-$. For $b\to c\tau \bar\nu$ we complement these with either an SU(2) singlet $S_1^\tau$ or doublet $R_2^\tau$ and study further the cases that also these Leptoquarks come in three replicas. The fixed point solutions for the $S_3^\ell$ couplings explain the $b\to s \ell^+\ell^-$ data for $S_3^{e,\mu}$ masses around 10 TeV. $b\to c\tau \bar\nu$ data can only be fully explained by couplings exceeding their fixed-point values and evolving into Landau poles at high energies, so that one can place an upper bound on $M_{QLU}$ between $10^{8}$ and $10^{11}$ GeV.Comment: 26 pages, 4 figures. Comments are welcome

A systematic study of phenomenological implications of dim-6 operators

The Standard Model (SM) of particle physics has been producing reliable estimates to a high precision level in the last few decades. Moreover, the discovery of a scalar particle with properties consistent with the SM Higgs boson, together with the fact that no Beyond Standard Model (BSM) particle has been detected so far, suggests that the New Physics (NP) scale Lambda can be placed above the electro-weak symmetry breaking (EWSB) scale. Therefore, an effective field theory built solely using the SM fields, called Standard Model Effective Field Theory (SMEFT), can be used to describe the low energy limit of BSM physics. This theory should be written adding to the renormalizable SM interactions further terms of higher dimensions, suppressed by suitable powers of the scale Lambda and invariant under the SM gauge group. The schematic Lagrangian is L_SMEFT = LSM + L_5 + L_6 + ... L_5 contains only the Weinberg operator, which can be used to provide masses to neutrinos. Assuming the conservation of baryon number, in L_6 there are 59 operators, many of which have flavour indices (explicitly taking them into account, the number of operators grows up to 2499). The full one-loop anomalous dimension (AD) matrix needed for renormalization group evolution (RGE) of the dimension 6 operators has been recently computed; several entries have been found to be of order 1, therefore suggesting a relevant mixing between some of these operators. The SMEFT approach can be used to interpret several patterns of deviations in SM processes: it allows for model independent analysis, which is a particularly useful feature given our present lack of knowledge regarding the ultraviolet (UV) completion of the SM theory. The BSM fields can in fact be integrated out of the theory at the NP scale, in such a way that there is no evident sign of their presence at the EWSB scale, but their effects can be mimicked by means of the couplings of the higher dimension operators; it will therefore be possible to use experimental informations in order to constrain the bounds of the such couplings, which can be consequently reinterpreted as bounds on the NP scale once the SMEFT is mapped on the desired UV completion of the theory. In my PhD project, I have focused my attention to phenomenological implications due to the effect of dimension 6 operators. As a first step of my project, I have partially recomputing the AD, in order to check the correctness of their results. Subsequently, I have been involved in analyses concerning the status of the anomalies present in B physics, with a particular focus on b to s transitions. My work on the field, aiming at discerning the shape of the potential NP underling such processes and potentially disentangling it from effects stemming from QCD effects, is reported in Refs.~\cite{Ciuchini:2015qxb,Ciuchini:2016weo,Ciuchini:2017gva,Ciuchini:2017mik}. A systematic reinterpretation of such findings in the SMEFT framework is an original contribution to this PhD thesis, and is yet to be published. Moreover, I have spent some time working on the study of the trilinear Higgs self-coupling. Given the large room for NP effects to such coupling, induced by the present status of the experimental constraints, the (SM)EFT approach is not a phenomenologically-meaningful framework to employ in order to study potential BSM effects in this sector. Therefore, I have adopted an alternative method to approach the matter, exploiting the study of electroweak precision observables in order to further constrain the bound that can be put on the Higgs trilinear self-coupling~\cite{Degrassi:2017ucl}

Effetti della densità di semina e della concimazione azotata sulla produzione del triticale

In the year 1981-82 a factorial trial of nitrogen fertilization (80, 120, 160, kg ha-1of N) and sowing rates (300, 350, 400 viable seeds per m2) has been carried out on three triticale lines in two environments of Sardinia (Oristano and Sassari). Equal N rates have been applied to a durum wheat at 350 sowing rate. The limited water availability in the soil, especially during the grain filling, has negatively affected the DM accumulation processes more markedly in the high ear n. per m2 thesis. In both sites the n. of plants increased with increase in seed rates and there was a greater correspondence between theoretical and reaI density at Oristano. Indipendently of the varieties and N rates, at Sassari yields have been slightly increasing with increase in sowing rates to which variations in the ear n. per m2 correspond in the same way, while at Oristano significant production increase has been achieved only by N80 rate owing to the seed rate. At Sassari, indipendent of sowing rates, triticale grain yields have been slightly increasing with increase in N rates. At Oristano production variation has not been achieved with lower sowing rates, decrease has been observed with more then N 80 kg ha-1 at higher sowing rate. A slightly higher triticale grain production compared with durum wheat has been achieved restricted to Oristano